This invention relates to systems for handling liquids moving through conduits wherein solid materials are likely to be carried by the liquids. The invention is particularly directed to the provision of a strainer screen located in the conduit.
Steam turbine generator systems are typical of systems of the type referred to. In such operations, steam is produced and fed to a turbine, and the output of the turbine is pumped back to the steam generator with the steam produced again entering the turbine. Systems of this type comprise so-called "closed" systems, and it is desirable to minimize to the extent reasonably possible the presence of any solids in the liquid utilized in the system. For that reason, strainer screens are located in the conduits whereby the circulating liquid will continuously pass through the screen and whereby solid materials can be collected by the screen and removed from the system.
Means for cleaning the strainer screens to periodically separate solids completely from the system are often utilized. Such systems also may provide for removal of a strainer screen after a period of time since the proportion of solids in the system can gradually be reduced to a tolerable level particularly where the system is completely closed.
Prior strainer screens have included metal frames having screening material extending between the frame edges. Such systems have also included screening materials of different mesh located in overlying relationship. Typically, a prior art construction included a pair of U-shaped channels attached at their ends to form an enclosed frame. The layers of screening material would then be tack welded at a plurality of points to the frame. Stainless steel is typically utilized for both the frame and screening material in view of the corrosive conditions that can prevail in systems of the type referred to. This tack welding between the heavy section frame and the fine wire of the screen is unsatisfactory. The wire frequently is melted and broken in the weld area. This type of welds are always very weak and subject to failure.
Particularly where high performance systems are involved, for example in nuclear plants, very high operating pressures can be developed. It has been found that the forces generated can actually tear the screening material away from the surrounding frame. This provides a highly undesirable condition since a system may then operate for some time without the benefit of the strainer screen and thereby lead to damage or inefficient operation of the system.
It has also been found that strainer screens of prior art design are not effective from the standpoint of efficient removal of solids from a system. Specifically, the mechanisms employed for periodically cleaning a screen to remove solids are often ineffective whereby solids remain in the screen even after a cleaning operation. This reduces the flow efficiency in the system.